(1) Field of Invention
This invention relates to nonaqueous liquid fabric treating compositions. More particularly, this invention relates to nonaqueous liquid laundry detergent compositions which are stable against phase separation and gelation and are easily pourable and to the use of these compositions for cleaning soiled fabrics, especially at elevated wash temperatures.
More specifically, the present invention relates to cleaning compositions adapted for use in the wash cycle of a laundering operation, especially using hot water. The composition includes a nonionic surfactant and an amphoteric surfactant to increase the high temperature cleaning performance of the nonionic surfactant.
(2) Discussion of Prior Art
Liquid nonaqueous heavy duty laundry detergent compositions are well known in the art. While many of the prior art detergent formulations provide satisfactory cleaning under many different conditions they still suffer from the defects of not providing adequate cleaning performance under hot water washing conditions, i.e. at temperatures of 60.degree. C. and higher. For instance, compositions of that type may comprise a liquid nonionic surfactant in which are dispersed particles of a builder, as shown for instance in the U.S. Pat. Nos. 4,316,812, 3,630,929 and 4,264,466 and British Patent Nos. 1,205,711, 1,270,040 and 1,600,981.
A related pending application and U.S. Patent assigned to the common assignee are Ser. No. 646,604, filed Aug. 31, 1984; and U.S. Pat. No. 4,622,173.
The application Ser. No. 646,604 discloses a dry powder composition, comprising a nonionic surfactant detergent, a quaternary ammonium salt softener and an amphoteric surfactant having improved softening and cleaning performance.
The U.S. Pat. No. 4,622,173 is directed to liquid nonaqueous nonionic laundry detergent compositions and broadly discloses that an amphoteric surfactant can be added to the composition.
Additional patents of interest are the Hellsten et al. U.S. Pat. Nos. 3,850,831 and Bus et al. 4,326,979. The patents disclose liquid nonaqueous nonionic laundry detergent compositions and broadly mention that an amphoteric surfactant can be added to the compositions.
Although it is not uncommon for present day laundry detergent compositions and for conventional home automatic washing machines, especially in the United States, to be able to effect washing/cleaning of soiled fabrics using cold or warm wash water, especially for sensitive fabrics, wash-wear fabrics, permanent-press fabrics, and the like, it is nevertheless appreciated that more effective cleaning (soil removal) requires higher washing temperatures. Furthermore, in Europe and in other countries, the home washing machines operate at hot temperatures of 60.degree. C. or 90.degree. C. or more, up to 100.degree. C. the boiling temperature of the wash water. These high temperatures are very beneficial for soil removal.
Liquid detergents are often considered to be more convenient to employ than dry powdered or particulate products and, therefore, have found substantial favor with consumers. They are readily measurable, speedily dissolved in the wash water, capable of being easily applied in concentrated solutions or dispersions to soiled areas on garments to be laundered and are non-dusting, and they usually occupy less storage space. Additionally, the liquid detergents may have incorpoated in their formulations materials which could not stand drying operations without deterioration, which materials are often desirably employed in the manufacture of particulate detergent products. Although they are possessed of many advantages over unitary or particulate solid products, liquid detergents often have certain inherent disadvantages too, which have to be overcome to produce acceptable commercial detergent products. Thus, some such products separate out on storage and others separate out on cooling and are not readily redispersed. In some cases the product viscosity changes and it becomes either too thick to pour or so thin as to appear watery. Some clear products become cloudy and others gel on standing.
The present inventors have discovered that cleaning performance of a nonaqueous liquid detergent composition based on a mixture of a nonionic detergent is significantly increased at elevated temperatures by the addition to the composition of amphoteric surfactants. Furthermore, the increased cleaning performance at elevated temperatures is achieved without any, or at least without any significant, deterioration in washing (i.e., cleaning) performance at lower temperatures (i.e., temperatures of 20.degree. to 40.degree. C.).
Applicants have discovered that the mixed nonionic/amphoteric surfactant compositions act synergistically to provide unexpected improved cleaning performance as compared to the same or greater amounts of each of the two surfactants used in the absence of the other.
Accordingly, it was totally unexpected that the cleaning performance of the nonionic surfactant could be dramatically improved at elevated temperatures, without diminishing cleaning performance at lower temperatures by adding an amphoteric surfactant to the nonionic surfactant detergent composition.
The present inventors have also been involved in studying the behavior of nonionic liquid surfactant systems with particulate matter suspended therein. Of particular interest has been nonaqueous built laundry liquid detergent compositions and the problem of settling of the suspended builder and other laundry additives as well as the problem of gelling associated with nonionic surfactants. These considerations have an impact on, for example, product stability, pourability and dispersibility.
It is known that one of the major problems with built liquid laundry detergents is their physical stability. This problem stems from the fact that the density of the solid particles dispersed in the nonionic liquid surfactant is higher than the density of the liquid surfactant.
Therefore, the dispersed particles tend to settle out. Two basic solutions exist to solve the settling out problem: increase nonionic liquid viscosity and reduce the dispersed solid particle size.
It is known that suspensions can be stabilized against settling by adding inorganic or organic thickening agents as dispersants, such as, for example, very high surface area inorganic materials, e.g. finely divided silica, clays, etc., organic thickeners, such as the cellulose ethers, acrylic and acrylamide polymers, polyelectrolytes, etc. However, such increases in suspension viscosity are naturally limited by the requirement that the liquid suspension be readily pourable and flowable, even at low temperature. Furthermore, these additives do not contribute to the cleaning performance of the formulation.
Grinding to reduce the particle size provides the following advantages:
1. Specific surface area of the dispersed particles is increased, and, therefore, particle wetting by the nonaqueous vehicle (liquid nonionic) is proportionately improved.
2. The average distance between dispersed particles is reduced with a proportionate increase in particle-to-particle invention. Each of these effects contributes to increase the rest-gel strength and the suspension yield stress while at the same time, grinding significantly reduces plastic viscosity.
The yield stress is defined as the minimum stress necessary to induce a plastic deformation (flow) of the suspension. Thus, visualizing the suspension as a loose network of dispersed particles, if the applied stress is lower than the yield stress, the suspension behaves like an elastic gel and no plastic flow will occur. Once the yield stress is overcome, the network breaks at some points and the sample begins to flow, but with a very high apparent viscosity. If the shear stress is much higher than the yield stress, the pigments are partially shear-deflocculated and the apparent viscosity decreases. Finally, if the shear stress is much higher than the yield stress value, the dispersed particles are completely shear-deflocculated and the apparent viscosity is very low, as if no particle interaction were present.
Therefore, the higher the yield stress of the suspension, the higher the apparent viscosity at low shear rate and the better is the physical stability against settling of the product.
In addition to the problem of settling or phase separation, the nonaqueous liquid laundry detergents based on liquid nonionic surfactants suffer from the drawback that the nonionics tend to gel when added to cold water. This is a particularly important problem in the ordinary use of European household automatic washing machines where the user places the laundry detergent composition in a dispensing unit (e.g. a dispensing drawer) of the machine. During the operation of the machine the detergent in the dispenser is subjected to a stream of cold water to transfer it to the main body of wash solution. Especially during the winter months when the detergent composition and water fed to the dispenser are particularly cold, the detergent viscosity increases markedly and a gel forms. As a result some of the composition is not flushed completely off the dispenser during operation of the machine, and a deposit of the composition builds up with repeated wash cycles, eventually requiring the user to flush the dispenser with hot water.
The gelling phenomenon can also be a problem whenever it is desired to carry out washing using cold water as may be recommended for certain synthetic and delicate fabrics or fabrics which can shrink in warm or hot water.
The tendency of concentrated detergent compositions to gel during storage is aggravated by storing the compositions in unheated storage areas, or by shipping the compositions during winter months in unheated transportation vehicles.
Partial solutions to the gelling problem have been proposed, for example, by diluting the liquid nonionic with certain viscosity controlling solvents and gel-inhibiting agents, such as lower alkanols, e.g. ethyl alcohol (see U.S. Pat. No. 3,953,380), alkali metal formates and adipates (see U.S. Pat. No. 4,368,147), hexylene glycol, polyethylene glycol, etc. and nonionic structure modification and optimization. As an example of nonionic surfactant modification one particularly successful result has been achieved by acidifying the hydroxyl moiety end group of the nonionic molecule. The advantages of introducing a carboxylic acid at the end of the nonionic include gel inhibition upon dilution; decreasing the nonionic pour point; and formation of an anionic surfactant when neutralized in the washing liquor. Nonionic structure optimization has centered on the chain length of the hydrophobic-lipophilic moiety and the number and make-up of alkylene oxide (e.g. ethylene oxide) units of the hydrophilic moiety. For example, it has been found that a C.sub.13 fatty alcohol ethoxylated with 8 moles of ethylene oxide presents only a limited tendency to gel formation.
Nevertheless, improvements are desired in both the stability and gel inhibition and in the high temperature cleaning performance of nonaqueous liquid fabric treating compositions.